Separating olefin streams

ABSTRACT

This invention pertains to separating an olefin stream into at least two olefin streams. The olefin stream that is to be separated is low in diene composition, which allows the olefin stream to be compressed at a relatively high temperature without causing fouling problems in the compressor system. The invention is particularly relevant to separating olefins obtained from an oxygen to olefins unit.

FIELD OF THE INVENTION

This invention relates to a process and system for separating an olefinstream into at least two olefin streams. More specifically, thisinvention relates to compressing an olefin product stream from anoxygenate to olefins unit and separating the compressed olefin streaminto at least two olefin streams.

BACKGROUND OF THE INVENTION

Olefins are conventionally produced through the process of steam orcatalytic cracking of various hydrocarbons. Olefins can also be producedby catalytically converting oxygenates to olefin compounds. The olefinproduct of such processes includes numerous olefin components (i.e.,compounds), as well as certain non-olefin components, which have to beseparated for further conversion to other chemical compounds such asolefin dimers, oligomers or polymers.

Conventional processes for separating olefin streams into other olefincomponent streams include compressing the olefin stream prior toseparation into the other component streams. These processes typicallyinvolve multi-stage compression processes, which require several largecompressors, and the compressed olefin stream is cooled after each stagewith intercoolers.

U.S. Pat. No. 6,444,869 discloses one type of process for the separationand recovery of ethylene and heavier components from an oxygenateconversion process. The oxygenate conversion effluent stream, whichcomprises hydrogen, carbon dioxide, water, C₂ to C₄ hydrocarbons andoxygenates, is withdrawn from the oxygenate conversion reactor andpassed to a multi-stage effluent compressor to raise the pressure of theoxygenate conversion effluent stream to provide a compressed effluentstream. The compressed effluent stream is passed to an oxygenate removalzone for the recovery of various oxygenates to provide an oxygenatedepleted effluent stream. The oxygenate depleted effluent stream ispassed to a carbon dioxide removal zone, and then to a dryer zone. Thedry effluent is passed to a series of fractionation zones to separatethe individual olefins into high purity products.

U.S. Pat. No. 6,441,261 discloses making an olefin stream by contactingoxygenate with a molecular sieve catalyst, compressing the olefinstream, and separating olefin components from the olefin stream. Theolefin product stream is compressed in a compressor comprising one tofour stages with cooling of the material between stages (intercooling).Higher compression ratios are considered to be desirable in that theyresult in less expensive compression modules, but are generally limitedto the extent that contaminants present in the olefin stream can causefouling at high temperatures. However, oxygenate conversion processesare considered to provide far fewer fouling contaminants, meaning thathigher compression ratios can be achieved.

Improved processes for separating olefin streams into other olefinstreams containing various olefin components are desired. In particular,processes which minimize compressor fouling or reducing the number ofcompressor stages used in separating olefin components in an olefinstream are sought.

SUMMARY OF THE INVENTION

This invention provides an improved process for separating an olefinstream into at least two olefin streams. The invention provides a way tominimize compressor fouling, as well as a way to reduce the number ofcompression stages.

In one embodiment, the invention comprises a process for separating anolefin stream into at least two olefin streams. The process comprisesproviding an olefin stream, wherein the olefin stream contains notgreater than about 3.0 wt % dienes, based on total weight of the olefinstream. The olefin stream is compressed in a compressor system having afirst stage and a second stage to obtain a compressed olefin stream, andthe compressed olefin stream is separated into at least two olefinstreams.

In another embodiment of the invention, the compressed olefin streamexits the first stage and the second stage at a temperature of notgreater than 260° F. (127° C.). Preferably, the compressed olefin streamexits the first stage and the second stage at a temperature of notgreater than 250° F. (121° C.). More preferably, the compressed olefinstream exits the first stage and the second stage at a temperature offrom 220° F. (104° C.) to 260° F. (127° C.). Still more preferably, thecompressed olefin stream exits the first stage and the second stage at atemperature of from 230° F. (110° C.) to 250° F. (121° C.).

In yet another embodiment of the invention, the compressed olefin streamexits the second stage at a pressure of at least 175 psia (1,207 kPa).Preferably, the compressed olefin stream exits the second stage at apressure of at least 200 psia (1,379 kPa).

In another embodiment, the compressed olefin stream exits the firststage at a pressure of from 75 psia (517 kPa) to 150 psia (1,034 kPa).Preferably, the compressed olefin stream exits the first stage at apressure of from 80 psia (552 kPa) to 140 psia (965 kPa).

The provided olefin can come from any source as long as the dieneconcentration is not too high. Such an olefin stream includes, as oneexample, an olefin stream made by contacting an oxygenate with amolecular sieve catalyst.

In one embodiment, the provided olefin stream comprises at least 50 wt %ethylene and propylene, based on total weight of the olefin stream. Inanother example, the provided olefin stream comprises from 50 wt % to 90wt % ethylene and propylene, based on total weight of the olefin stream.

In another embodiment of the invention, the at least two olefin streamswhich are separated from the provided olefin include a light olefinstream and a heavy olefin stream. Desirably, the light olefin streamcomprises at least one olefin selected from the group consisting ofethylene, propylene and butylenes, and the heavy olefin stream comprisesolefins that have boiling points that are, on average, higher than thosein the light olefin stream.

This invention includes an optional step of treating the compressedolefin stream between the first stage and the second stage of thecompression system to remove acid gases prior to separating thecompressed olefin stream into at least two olefin streams. Alsooptionally included is a step of washing the compressed olefin withwater prior to separating into the at least two olefin streams. A stepof drying the compressed olefin stream is also optionally included.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic drawing showing one embodiment of a flow scheme ofthe invention in which an olefin stream is compressed in a two stagecompressor, and the compressed olefin stream is separated into a lightolefin steam and a heavy olefin stream.

DETAILED DESCRIPTION OF THE INVENTION I. Introduction

This invention provides a process for separating an olefin stream intoat least two olefin streams. The process is performed with a minimalnumber of compression stages to compress the olefin stream to a pressureat which the compressed olefin stream can be efficiently separated intoat least a light olefin stream and a heavy olefin stream.

The number of compression stages can be reduced in this invention,compared to that of conventional systems, since the amount of dienecomponents in the olefin stream that is to be compressed is limited. Bylimiting the amount of dienes in the olefin stream, the compressionsystem can be operated at higher than conventional temperatures, with asignificant reduction in compressor fouling problems. An olefin streamhaving a high diene concentration will cause significant compressorfouling problems at high compression temperatures.

II. Olefin Stream that is to be Compressed

In this invention, an olefin stream is compressed and separated into atleast two olefin streams. The two olefin streams preferably include atleast a light olefin stream and a heavy olefin stream. The light olefinstream comprises at least one olefin selected from the group consistingof ethylene, propylene and butylene. The heavy olefin stream comprisesolefins that have boiling points that are, on average, higher than thosein the light olefin stream.

The olefin stream that is to be compressed and separated contains notgreater than about 3.0 wt % dienes, particularly dienes such asbutadienes and pentadienes, based on total weight of the olefin stream.Preferably, the olefin stream that is to be separated contains notgreater than about 2.0 wt % dienes, more preferably not greater thanabout 1.0 wt % dienes, and most preferably not greater than about 0.5 wt% dienes, based on total weight of the olefin stream.

The olefin stream that is to be compressed and separated into olefincomponents is optionally relatively low in water content, as too muchwater can cause problems in compressor efficiency and/or operation.Desirably, the olefin stream contains not greater than about 10 wt %water, based on total weight of the olefin stream. Preferably, theolefin stream contains not greater than about 5 wt % water, and morepreferably not greater than about 3 wt % water, based on total weight ofthe olefin stream.

In one embodiment of the invention, the olefin stream that is to becompressed and separated is relatively high in light olefins such asethylene, propylene, and butylene. Preferably, the olefin stream has asubstantial quantity of ethylene and propylene.

In one embodiment of the invention, the olefin stream that is to becompressed and separated comprises at least about 25 wt % ethylene,based on total weight of the olefin stream. Preferably, the olefinstream comprisesfrom about 25 wt % ethylene to about 75 wt % ethylene,more preferably from about 30 wt % to about 60 wt % ethylene, and mostpreferably from about 35 wt % to about 50 wt % ethylene, based on totalweight of the olefin stream.

In another embodiment, the olefin stream that is to be compressed andseparated also comprises at least about 20 wt % propylene, based ontotal weight of the olefin stream. Preferably, the provided olefinstream comprises from about 20 wt % to about 70 wt % propylene, morepreferably from about 25 wt % to about 50 wt % propylene, and mostpreferably from about 30 wt % to about 40 wt % propylene, based on totalweight of the olefin stream.

It is desirable, but not required, that the provided olefin stream thatis to be compressed and separated contain a relatively low concentrationof ethane, preferably a lower concentration of ethane than propane,which can also be present. Preferably, the olefin stream comprises notgreater than about 4 wt % ethane, more preferably not greater than about3 wt % ethane, and most preferably not greater than about 2 wt % ethane,based on total weight of the olefin stream.

It is also desirable, but not required, that the provided olefin streamthat is to be compressed and separated into olefin components contain arelatively low concentration of propane. Preferably, the olefin streamcomprises not greater than about 5 wt % propane, more preferably notgreater than about 4 wt % propane, and most preferably not greater thanabout 3 wt % propane, based on total weight of the olefin stream.

In another embodiment of the invention, the provided olefin stream thatis to be compressed and separated into olefin components contains bothethylene and propylene. Desirably, the olefin stream contains at leastabout 50 wt % ethylene and propylene, based on total weight of theolefin stream. Preferably, the olefin stream contains from about 50 wt %to about 95 wt % ethylene and propylene, more preferably from about 55wt % to about 90 wt % ethylene and propylene, and most preferably fromabout 60 wt % to about 85 wt % ethylene and propylene, based on totalweight of the olefin stream.

III. Description of the Olefin Stream that is to be Compressed andSeparated

The olefin stream that is to be compressed and separated into olefincomponents can come from any source as long as the diene concentrationis not too high. Such sources include cracking of hydrocarbons to formolefins, and catalytic conversion of oxygenates to olefins. Olefinsobtained from the catalytic conversion of oxygenates to olefins arepreferred as additional diene and other separation processes can beavoided. It is also acceptable to combine olefin streams from multiplesources as long as the diene concentration of the stream remainsrelatively low.

In one embodiment of the invention, the olefin stream that is to beseparated into olefin components is obtained by contacting oxygenatewith an olefin producing catalyst. Preferably, the olefin producingcatalyst is a molecular sieve catalyst.

The oxygenate that is used in forming the olefin stream comprises atleast one organic compound which contains at least one oxygen atom, suchas aliphatic alcohols, ethers, carbonyl compounds (aldehydes, ketones,carboxylic acids, carbonates, esters and the like). When the oxygenateis an alcohol, the alcohol includes an aliphatic moiety having from 1 to10 carbon atoms, more preferably from 1 to 4 carbon atoms.Representative alcohols include but are not necessarily limited to lowerstraight and branched chain aliphatic alcohols and their unsaturatedcounterparts. Examples of suitable oxygenate compounds include, but arenot limited to: methanol; ethanol; n-propanol; isopropanol; C₄-C₂₀alcohols; methyl ethyl ether; dimethyl ether; diethyl ether;di-isopropyl ether; formaldehyde; dimethyl carbonate; dimethyl ketone;acetic acid; and mixtures thereof. Preferred oxygenate compounds aremethanol, dimethyl ether, or a mixture thereof.

Molecular sieves capable of converting an oxygenate to an olefincompound include zeolites as well as non-zeolites, and are of the large,medium or small pore type. Small pore molecular sieves are preferred inone embodiment of this invention, however. As defined herein, small poremolecular sieves have a pore size of less than about 5.0 angstroms.Generally, suitable catalysts have a pore size ranging from about 3.5 toabout 5.0 angstroms, preferably from about 4.0 to about 5.0 angstroms,and most preferably from about 4.3 to about 5.0 angstroms.

Zeolite materials, both natural and synthetic, have been demonstrated tohave catalytic properties for various types of hydrocarbon conversionprocesses. In addition, zeolite materials have been used as adsorbents,catalyst carriers for various types of hydrocarbon conversion processes,and other applications. Zeolites are complex crystallinealuminosilicates which form a network of AlO₂ and SiO₂ tetrahedra linkedby shared oxygen atoms. The negativity of the tetrahedra is balanced bythe inclusion of cations such as alkali or alkaline earth metal ions. Inthe manufacture of some zeolites, non-metallic cations, such astetramethylammonium (TMA) or tetrapropylammonium (TPA), are presentduring synthesis. The interstitial spaces or channels formed by thecrystalline network enable zeolites to be used as molecular sieves inseparation processes, as catalyst for chemical reactions, and ascatalyst carriers in a wide variety of hydrocarbon conversion processes.

Zeolites include materials containing silica and optionally alumina, andmaterials in which the silica and alumina portions have been replaced inwhole or in part with other oxides. For example, germanium oxide, tinoxide, and mixtures thereof can replace the silica portion. Boron oxide,iron oxide, gallium oxide, indium oxide, and mixtures thereof canreplace the alumina portion. Unless otherwise specified, the terms“zeolite” and “zeolite material” as used herein, shall mean not onlymaterials containing silicon atoms and, optionally, aluminum atoms inthe crystalline lattice structure thereof, but also materials whichcontain suitable replacement atoms for such silicon and aluminum atoms.

One type of olefin forming catalyst capable of producing largequantities of ethylene and propylene is a silicoaluminophosphate (SAPO)molecular sieve. Silicoaluminophosphate molecular sieves are generallyclassified as being microporous materials having 8, 10, or 12 memberedring structures. These ring structures can have an average pore sizeranging from about 3.5 to about 15 angstroms. Preferred are the smallpore SAPO molecular sieves having an average pore size of less thanabout 5 angstroms, preferably an average pore size ranging from about3.5 to about 5 angstroms, more preferably from about 3.5 to about 4.2angstroms. These pore sizes are typical of molecular sieves having 8membered rings.

According to one embodiment, substituted SAPOs can also be used inoxygenate to olefin reaction processes. These compounds are generallyknown as MeAPSOs or metal-containing silicoaluminophosphates. The metalcan be alkali metal ions (Group IA), alkaline earth metal ions (GroupHA), rare earth ions (Group HIB, including the lanthanoid elements:lanthanum, cerium, praseodymium, neodymium, samarium, europium,gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium andlutetium; and scandium or yttrium) and the additional transition cationsof Groups IVB, VB, VIIB, VIIB, VIIIB, and IB.

Preferably, the Me represents atoms such as Zn, Mg, Mn, Co, Ni, Ga, Fe,Ti, Zr, Ge, Sn, and Cr. These atoms can be inserted into the tetrahedralframework through a [MeO₂] tetrahedral unit. The [MeO₂] tetrahedral unitcarries a net electric charge depending on the valence state of themetal substituent. When the metal component has a valence state of +2,+3, +4, +5, or +6, the net electric charge is between −2 and +2.Incorporation of the metal component is typically accomplished addingthe metal component during synthesis of the molecular sieve. However,post-synthesis ion exchange can also be used. In post synthesisexchange, the metal component will introduce cations into ion-exchangepositions at an open surface of the molecular sieve, not into theframework itself.

Suitable silicoaluminophosphate molecular sieves include SAPO-5, SAPO-8,SAPO-11, SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35,SAPO-36, SAPO-37, SAPO-40, SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56,the metal containing forms thereof, and mixtures thereof. Preferred areSAPO-18, SAPO-34, SAPO-35, SAPO-44, and SAPO-47, particularly SAPO-18and SAPO-34, including the metal containing forms thereof, and mixturesthereof. As used herein, the term mixture is synonymous with combinationand is considered a composition of matter having two or more componentsin varying proportions, regardless of their physical state.

An aluminophosphate (ALPO) molecular sieve can also be included in thecatalyst composition. Aluminophosphate molecular sieves are crystallinemicroporous oxides which can have an AlPO₄ framework. They can haveadditional elements within the framework, typically have uniform poredimensions ranging from about 3 angstroms to about 10 angstroms, and arecapable of making size selective separations of molecular species. Morethan two dozen structure types have been reported, including zeolitetopological analogues. A more detailed description of the background andsynthesis of aliminophosphates is found in U.S. Pat. No. 4,310,440,which is incorporated herein by reference in its entirety. PreferredALPO structures are ALPO-5, ALPO-11, ALPO-18, ALPO-31, ALPO-34, ALPO-36,ALPO-37, and ALPO-46.

The ALPOs can also include a metal substituent in its framework.Preferably, the metal is selected from the group consisting ofmagnesium, manganese, zinc, cobalt, and mixtures thereof. Thesematerials preferably exhibit adsorption, ion-exchange and/or catalyticproperties similar to aluminosilicate, aluminophosphate and silicaaluminophosphate molecular sieve compositions. Members of this class andtheir preparation are described in U.S. Pat. No. 4,567,029, incorporatedherein by reference in its entirety.

The metal containing ALPOs have a three-dimensional microporous crystalframework structure of MO₂, Al0 ₂ and PO₂ tetrahedral units. These asmanufactured structures (which contain template prior to calcination)can be represented by empirical chemical composition, on an anhydrousbasis, as:

mR:(M_(X)Al_(y)P_(z))O₂

wherein “R” represents at least one organic templating agent present inthe intracrystalline pore system; “m” represents the moles of “R”present per mole of (M_(x)Al_(y)P_(z))O₂ and has a value of from zero to0.3, the maximum value in each case depending upon the moleculardimensions of the templating agent and the available void volume of thepore system of the particular metal aluminophosphate involved, “x”, “y”,and “z” represent the mole fractions of the metal “M”, (i.e. magnesium,manganese, zinc and cobalt), aluminum and phosphorus, respectively,present as tetrahedral oxides.

The metal containing ALPOs are sometimes referred to by the acronym asMeAPO. Also in those cases where the metal “Me” in the composition ismagnesium, the acronym MAPO is applied to the composition. SimilarlyZAPO, MnAPO and CoAPO are applied to the compositions which containzinc, manganese and cobalt respectively. To identify the variousstructural species which make up each of the subgeneric classes MAPO,ZAPO, CoAPO and MnAPO, each species is assigned a number and isidentified, for example, as ZAPO-5, MAPO-11, CoAPO-34 and so forth.

The silicoaluminophosphate molecular sieve is typically admixed (i.e.,blended) with other materials. When blended, the resulting compositionis typically referred to as a SAPO catalyst, with the catalystcomprising the SAPO molecular sieve.

Materials which can be blended with the molecular sieve can be variousinert or catalytically active materials, or various binder materials.These materials include compositions such as kaolin and other clays,various forms of rare earth metals, metal oxides, other non-zeolitecatalyst components, zeolite catalyst components, alumina or aluminasol, titania, zirconia, magnesia, thoria, beryllia, quartz, silica orsilica or silica sol, and mixtures thereof. These components are alsoeffective in reducing, inter alia, overall catalyst cost, acting as athermal sink to assist in heat shielding the catalyst duringregeneration, densifying the catalyst and increasing catalyst strength.It is particularly desirable that the inert materials that are used inthe catalyst to act as a thermal sink have a heat capacity of from about0.05 to about 1 cal/g-° C., more preferably from about 0.1 to about 0.8cal/g-° C., most preferably from about 0.1 to about 0.5 cal/g-° C.

Additional molecular sieve materials can be included as a part of theSAPO catalyst composition or they can be used as separate molecularsieve catalysts in admixture with the SAPO catalyst if desired.Structural types of small pore molecular sieves that are suitable foruse in this invention include AEI, AFT, APC, ATN, ATT, ATV, AWW, MK,CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV, LOV, LTA, MON, PAU,PHI, RHO, ROG, THO, and substituted forms thereof. Structural types ofmedium pore molecular sieves that are suitable for use in this inventioninclude MFI, MEL, MTW, EUO, MIT, HEU, FER, AFO, AEL, TON, andsubstituted forms thereof. These small and medium pore molecular sievesare described in greater detail in the Atlas of Zeolite StructuralTypes, W. M. Meier and D. H. Olsen, Butterworth Heineman, 3rd ed., 1997,the detailed description of which is explicitly incorporated herein byreference. Preferred molecular sieves which can be combined with asilicoaluminophosphate catalyst include ZSM-5, ZSM-34, erionite, andchabazite.

The catalyst composition, according to an embodiment, preferablycomprises from about 1% to about 99%, more preferably from about 5% toabout 90%, and most preferably from about 10% to about 80%, by weight ofmolecular sieve. It is also preferred that the catalyst composition havea particle size of from about 20 angstroms to about 3,000 angstroms,more preferably from about 30 angstroms to about 200 angstroms, mostpreferably from about 50 angstroms to about 150 angstroms.

The catalyst can be subjected to a variety of treatments to achieve thedesired physical and chemical characteristics. Such treatments include,but are not necessarily limited to hydrothermal treatment, calcination,acid treatment, base treatment, milling, ball milling, grinding, spraydrying, and combinations thereof.

A molecular sieve catalyst particularly useful in making ethylene andpropylene is a catalyst which contains a combination of SAPO-34, andSAPO-18 or ALPO-18 molecular sieve. In a particular embodiment, themolecular sieve is a crystalline intergrowth of SAPO-34, and SAPO-18 orALPO-18.

To convert oxygenate to olefin, conventional reactor systems can beused, including fixed bed, fluid bed or moving bed systems. Preferredreactors of one embodiment are co-current riser reactors and shortcontact time, countercurrent free-fall reactors. Desirably, the reactoris one in which an oxygenate feedstock can be contacted with a molecularsieve catalyst at a weight hourly space velocity (WHSV) of at leastabout 1 hr', preferably in the range of from about 1 hf⁻¹ to 1000 hr⁻¹,more preferably in the range of from about 20 hf⁻¹ to about 1000 hf⁻¹,and most preferably in the range of from about 50 hf⁻¹ to about 500hr⁻¹. WHSV is defined herein as the weight of oxygenate, and reactivehydrocarbon which may optionally be in the feed, per hour per weight ofthe molecular sieve in the reactor. Because the catalyst or thefeedstock may contain other materials which act as inerts or diluents,the WHSV is calculated on the weight basis of the oxygenate feed, andany reactive hydrocarbon which may be present with the oxygenate feed,and the molecular sieve contained in the reactor.

Preferably, the oxygenate feed is contacted with the catalyst when theoxygenate is in a vapor phase. Alternately, the process may be carriedout in a liquid or a mixed vapor/liquid phase. When the process iscarried out in a liquid phase or a mixed vapor/liquid phase, differentconversions and selectivities of feed-to-product may result dependingupon the catalyst and reaction conditions.

The process can generally be carried out at a wide range oftemperatures. An effective operating temperature range can be from about200° C. to about 700° C., preferably from about 300° C. to about 600°C., more preferably from about 350° C. to about 550° C. At the lower endof the temperature range, the formation of the desired olefin productsmay become markedly slow with a relatively high content of oxygenatedolefin by-products being found in the olefin product. However, theselectivity to ethylene and propylene at reduced temperatures may beincreased. At the upper end of the temperature range, the process maynot form an optimum amount of ethylene and propylene product, but theconversion of oxygenate feed will generally be high.

Operating pressure also may vary over a wide range, including autogenouspressures. Effective pressures include, but are not necessarily limitedto, a total pressure of at least about 1 psia (7 kPa), preferably atleast about 5 psia (34 kPa). The process is particularly effective athigher total pressures, including a total pressure of at least about 20psia (138 kPa). Preferably, the total pressure is at least about 25 psia(172 kPa), more preferably at least about 30 psia (207 kPa). Forpractical design purposes it is desirable to use methanol as the primaryoxygenate feed component, and operate the reactor at a pressure of notgreater than about 500 psia (3445 kPa), preferably not greater thanabout 400 psia (2756 kPa), most preferably not greater than about 300psia (2067 kPa).

Undesirable by-products can be avoided by operating at an appropriategas superficial velocity. As the gas superficial velocity increases theconversion decreases avoiding undesirable by-products. As used herein,the term, “gas superficial velocity” is defined as the combinedvolumetric flow rate of vaporized feedstock, which includes diluent whenpresent in the feedstock, as well as conversion products, divided by thecross-sectional area of the reaction zone. Because the oxygenate isconverted to a product having significant quantities of ethylene andpropylene while flowing through the reaction zone, the gas superficialvelocity may vary at different locations within the reaction zone. Thedegree of variation depends on the total number of moles of gas presentand the cross section of a particular location in the reaction zone,temperature, pressure and other relevant reaction parameters.

In one embodiment, the gas superficial velocity is maintained at a rateof greater than about 1 meter per second (m/s) at least one point in thereaction zone. In another embodiment, it is desirable that the gassuperficial velocity is greater than about 2 m/s at least one point inthe reaction zone. More desirably, the gas superficial velocity isgreater than about 2.5 m/s at least one point in the reaction zone. Evenmore desirably, the gas superficial velocity is greater than about 4 m/sat least one point in the reaction zone. Most desirably, the gassuperficial velocity is greater than about 8 m/s at least one point inthe reaction zone.

According to yet another embodiment of the invention, the gassuperficial velocity is maintained relatively constant in the reactionzone such that the gas superficial velocity is maintained at a rategreater than about 1 m/s at all points in the reaction zone. It is alsodesirable that the gas superficial velocity be greater than about 2 m/sat all points in the reaction zone. More desirably, the gas superficialvelocity is greater than about 2.5 m/s at all points in the reactionzone. Even more desirably, the gas superficial velocity is greater thanabout 4 m/s at all points in the reaction zone. Most desirably, the gassuperficial velocity is greater than about 8 m/s at all points in thereaction zone.

The amount of ethylene and propylene produced in the oxygenate to olefinprocess can be increased by reducing the conversion of the oxygenates inthe oxygenate to olefins reaction. However, reducing the conversion offeed oxygenates in the oxygenate conversion reaction tends to increasethe amount of oxygenated hydrocarbons, particularly including dimethylether, that are present in the olefin product. Thus, control of theconversion of feed to the oxygenate reaction process can be important.

According to one embodiment, the conversion of the primary oxygenate,e.g., methanol, is from about 90 wt % to about 98 wt %. According toanother embodiment the conversion of methanol is from about 92 wt % toabout 98 wt %, preferably from 94 wt % to 98 wt %.

According to another embodiment, the conversion of methanol is aboveabout 98 wt % to less than about 100 wt %. According to anotherembodiment, the conversion of methanol is from about 98.1 wt % to lessthan about 100 wt %; preferably from about 98.2 wt % to about 99.8 wt %.According to another embodiment, the conversion of methanol is fromabout 98.2 wt % to less than about 99.5 wt %; preferably from about 98.2wt % to about 99 wt %.

In this invention, weight percent conversion is calculated on a waterfree basis unless otherwise specified. Weight percent conversion on awater free basis is calculated as: 100× (weight oxygenate fed on a waterfree basis—weight oxygenated hydrocarbon in the product on a water freebasis). The water free basis of oxygenate is calculated by subtractingout the water portion of the oxygenate in the feed and product, andexcluding water formed in the product. For example, the weight flow rateof methanol on an oxygenate free basis is calculated by multiplying theweight flow rate of methanol by 14/32 to remove the water component ofthe methanol. As another example, the rate flow rate of dimethyl etheron an oxygenate free basis is calculated by multiplying the weight flowrate of diemethylether by 40/46 to remove the water component of thedimethyl ether. If there is a mixture of oxygenates in the feed orproduct, trace oxygenates are not included. When methanol and/ordimethyl ether is used as the feed, only methanol and dimethyl ether areused to calculate conversion on a water free basis.

In this invention, selectivity is also calculated on a water free basisunless otherwise specified. Selectivity is calculated as: 100× wt %component/(100-wt % water-wt % methanol-wt % dimethyl ether) whenmethanol and/or dimethyl ether is used as the feed.

The oxygenate to olefin process forms a substantial amount of water as aby-product. Much of this water by-product can be removed prior todistillation by cooling the stream to a temperature below thecondensation temperature of the water vapor in the stream. Preferably,the temperature of the product stream is cooled to a temperature belowthe condensation temperature of the oxygenate feed. In certainembodiments it is desirable to cool the product stream below thecondensation temperature of methanol.

It is desirable to cool the olefin stream from the oxygenate to olefinreaction process, then separate the cooled olefin stream into acondensed, water containing stream and an olefin vapor stream. Thecondensed, water containing stream comprises most of the water from theolefin stream, and a significant portion of the oxygenated hydrocarbonsfrom the olefin stream. The olefin vapor stream comprises a majority ofthe olefins, e.g., ethylene and propylene. This olefin vapor stream willbe in condition to send to the compressor system for compression andseparation into olefin component streams. Such a stream will be have theacceptable diene content so that compressor fouling can be minimized.

A quench column is one type of equipment that is effective in coolingthe olefin stream from the olefin to oxygenate reaction process. In aquench column, a quenching fluid is directly contacted with the olefinstream to cool the stream to the desired condensation temperature.Condensation produces the condensed water containing stream, which isalso referred to as a heavy bottoms stream. The olefin portion of theolefin product stream remains a vapor, and exits the quench column as anoverhead vapor stream. The overhead vapor stream is rich in olefinproduct, and can also contain some oxygenated hydrocarbon by-products aswell as water.

In one embodiment, the quenching fluid is a recycle stream of thecondensed water containing, heavy bottoms stream of the quench column.This water containing stream is desirably cooled, e.g., by a heatexchanger, and injected back into the quench column. It is preferred inthis embodiment to not inject cooling medium from an outside source intothe quench column, although it may be desirable to do so in otherseparation equipment down stream of the quench column.

IV. Compressing the Olefin Stream

In one embodiment of the invention, the olefin stream that is to beseparated into at least two olefin streams is compressed in a compressorsystem having a first stage and a second stage. In the compressionprocess, it is desirable that the compressed olefin stream exit thecompressor system at both the first stage and the second stage at atemperature of not greater than about 260° F. (127° C.). Preferably, thecompressed olefin stream exits the first stage and the second stage at atemperature of not greater than about 250° F. (121° C.). Morepreferably, the compressed olefin stream exits the first stage and thesecond stage of the compressor system at a temperature of from about220° F. (104° C.) to about 260° F. (127° C.), more preferably at atemperature of from about 230° F. (110° C.) to about 250° F. (121° C.).

It is desirable in this invention that the olefin stream be compressedto a pressure which is effective for separating lighter olefins,particularly ethylene and propylene, from heavier olefins in a firststage separation vessel. In this regard, it is desirable that thecompressed olefin stream exit the second stage of the compressor systemat a pressure of at least about 175 psia (1,207 kPa). Preferably, thecompressed olefin stream exits the second stage of the compressor systemat a pressure of at least about 190 psia (1,310 kPa), more preferably atleast about 200 psia (1,379 kPa). The second stage exit pressure islimited only by practical considerations, such as vessel thickness andexpense of the compressor system. An upper pressure limit of about 500psia (3,448 kPa) is a sufficient practical limit.

The pressure at which the olefin exits the first stage of the compressorsystem is only limited to the extent that the compressed olefin does notincrease to an undesirably high temperature in the compression system,as high temperatures can degrade product quality and cause other systemproblems. However, it is desirable to balance the size of the twocompressors used. In one embodiment, the olefin stream exits the firststage of the compressor system at a pressure of from about 75 psia (517kPa) to about 150 psia (1,034 kPa); preferably a pressure of from about80 psia (552 kPa) to about 140 psia (965 kPa); and most preferably apressure of from about 90 psia (620 kPa) to about 130 psia (896 kPa).

V. Acid Gas Treating the Compressed Olefin Stream

In one embodiment of the invention, the olefin stream that exits thefirst stage of the compressor system is also treated to remove entrainedacid gases such as CO₂ which may also be present in the olefin stream.Solid or liquid acid gas treatment systems can be used in thisinvention. In either system, the acid gas is removed from the compressedolefin stream by contacting the compressed olefin stream with an acidgas absorbent or adsorbent. Examples of such absorbents or adsorbentsinclude amines, potassium carbonate, caustic, alumina, molecular sieves,and membranes, particularly membranes formed of polysulfone, polyimid,polyamide, glassy polymer and cellulose acetate. Solutions containingamines and caustic compounds are preferred, with caustic compounds beingmore preferred.

Aqueous amine solutions which are useful in this invention can containany amine compound or compounds suitable for acid gas absorption.Examples include alkanolamines, such as triethanolamine (TEA);methyldiethanolamine (MDEA); diethanolamine (DEA); monoethanolamine(MEA); diisopropanolamine (DIPA); and hydroxyaminoethyl ether (DGA).Effective concentrations can range from about 0.5 to about 8 moles ofamine per liter of aqueous solution.

Piperazine and/or monomethylethanolamine (MMEA) can be added to aqueousamine solutions to enhance their absorption capabilities. Theseadditives can be included in the aqueous solution at a concentration offrom about 0.04 to about 2 moles per liter of aqueous solution.

Caustic compounds which can be used in this invention are alkalinecompounds which are effective in removing acid gas from an olefinstream. Examples of such alkaline compounds include sodium hydroxide andpotassium hydroxide.

VI. Washing and Drying the Compressed Olefin Stream

Following acid gas treating, it is desirable to remove additionallyentrained material in the treated compressed olefin steam using a waterwash. Conventional equipment can be used.

This invention further includes an optional drying embodiment. In thisembodiment, a solid or liquid drying system can be used to remove waterand/or additional oxygenated hydrocarbon from the olefin stream thatexits the second stage olefin compressor.

In the solid drying system, the compressed olefin stream is contactedwith a solid adsorbent to further remove water and oxygenatedhydrocarbon to very low levels. Typically, the adsorption process iscarried out in one or more fixed beds containing a suitable solidadsorbent.

Adsorption is useful for removing water and oxygenated hydrocarbons tovery low concentrations, and for removing oxygenated hydrocarbons thatmay not normally be removed by using other treatment systems.Preferably, an adsorbent system used as part of this invention hasmultiple adsorbent beds. Multiple beds allow for continuous separationwithout the need for shutting down the process to regenerate the solidadsorbent. For example, in a three bed system typically one bed ison-line, one bed is regenerated off-line, and a third bed is onstand-by.

The specific adsorbent solid or solids used in the adsorbent bedsdepends on the types of contaminants being removed. Examples of solidadsorbents for removing water and various polar organic compounds, suchas oxygenated hydrocarbons and absorbent liquids, include aluminas,silica, 3 Å molecular sieves, 4 Å molecular sieves, andalumino-silicates. Beds containing mixtures of these sieves or multiplebeds having different adsorbent solids can be used to remove water, aswell as a variety of oxygenated hydrocarbons.

In this invention, one or more adsorption beds can be arranged in seriesor parallel. In one example of a series arrangement, a first bed is usedto remove the smallest and most polar molecules which are the easiest toremove. Subsequent beds for removing larger less polar oxygenatedspecies are next in series. As a specific example of one type ofarrangement, water is first selectively removed using a 3 Å molecularsieve. This bed is then followed by one or more beds containing one ormore less selective adsorbents such as a larger pore molecular sievee.g. 13 X and/or a high surface area active alumina such as Selexorb CD(Alcoa tradename).

In another embodiment, the first bed is a 3.6 Å molecular sieve capableof selectively removing both water and methanol. This bed can then befollowed by one or more 13 X or active alumina beds as described above.

The adsorbent beds can be operated at ambient temperature or at elevatedtemperature as required, and with either upward or downward flow.Regeneration of the adsorbent materials can be carried out byconventional processes including treatment with a stream of a dry inertgas such as nitrogen at elevated temperature.

In the liquid drying system, a water absorbent is used to remove waterfrom the compressed olefin stream. The water absorbent can be any liquideffective in removing water from an olefin stream. Examples of waterabsorbents include alcohols, amines, amides, nitriles, heterocyclicnitrogen containing compounds, or a combination of any of the preceding.Either monohydric alcohols or polyhydric alcohols can be used as thealcohol absorbent. Specific examples of absorbents include methanol,ethanol, propanol, ethylene glycol, diethylene glycol, triethyleneglycol, ethanolamine, diethanolamine, triethanolamine, hindered cyclicamines, acetonitrile, n-methylpyrrolidone, dimethyl formamide, andcombinations thereof.

To obtain a substantial degree of effectiveness, the water absorbentshould contain little non-water absorbing components. For example, thewater absorbent should contain at least about 75 wt % water absorbingcomponents. Desirably, the water absorbent contains at least about 90 wt%, preferably at least about 95 wt %, and most preferably at least about98 wt % water absorbent.

Preferably the compressed olefin stream that is to be separated intoolefin components is sufficiently dried before entering the separationvessel so that free water formation (i.e., formation of a separate waterphase) or gas hydration does not significantly impede the separationprocess. Gas hydration results in the formation of clathrate compounds.Such compounds are solids, and these solids can cause significantoperational problems in the separation process.

Water that is present in the compressed olefin stream that enters theseparation vessel should be at a concentration sufficiently low suchthat a separate water phase is not formed during the separation process.This is particularly important when a distillation column having traysis used to separate the olefin components, since a separate water phaseformed in the trays will impede mass transfer. Distillation columnshaving packing are preferred at higher concentrations of water, sincesuch columns will not be prone to collect separate water phases.

It is desirable in this invention that the compressed olefin stream thatis to be separated into olefin components contain not greater than about10,000 wppm water, based on total weight of the olefin stream.Preferably the compressed olefin stream contains not greater than about1,000 wppm water, more preferably not greater than 500 wppm water, andmost preferably not greater than about 100 wppm water, based on totalweight of the olefin stream.

It is not necessary in this invention that the compressed olefin streambe completely dry to separate into olefin components. That is, thecompressed olefin stream can contain some water. The benefit of theolefin stream containing some amount of water is that additional and/orcomplex drying equipment will not be needed in order to separate theolefin stream into component products.

The compressed and optionally dried olefin stream is separated intoolefin components using conventional separation equipment. For example,conventional distillation columns can be used.

VII. Ethylene, Propylene and Butylene Recovery and Derivative Processes

The olefin stream is desirably separated into olefin components so thathigh purity ethylene and propylene can be recovered. According to thisinvention, high purity is defined as at least about 95 wt %. Preferably,the ethylene and propylene streams comprise at least about 98 wt %ethylene or propylene, and most preferably at least about 99 wt %ethylene or propylene.

The ethylene and propylene streams separated according to this inventioncan be polymerized to form plastic compositions, e.g., polyolefins,particularly polyethylene and polypropylene. Any conventional processfor forming polyethylene or polypropylene can be used. Catalyticprocesses are preferred. Particularly preferred are metallocene,Ziegler/Natta, aluminum oxide and acid catalytic systems. See, forexample, U.S. Pat. Nos. 3,258,455; 3,305,538; 3,364,190; 5,892,079;4,659,685; 4,076,698; 3,645,992; 4,302,565; and 4,243,691, the catalystand process descriptions of each being expressly incorporated herein byreference. In general, these processes involve contacting the ethyleneor propylene product with a polyolefin-forming catalyst at a pressureand temperature effective to form the polyolefin product.

In one embodiment of this invention, the ethylene or propylene productis contacted with a metallocene catalyst to form a polyolefin.Desirably, the polyolefin forming process is carried out at atemperature ranging between about 50° C. and about 320° C. The reactioncan be carried out at low, medium or high pressure, being anywherewithin the range of about 1 bar to about 3200 bar. For processes carriedout in solution, an inert diluent can be used. In this type ofoperation, it is desirable that the pressure be at a range of from about10 bar to about 150 bar, and preferably at a temperature range of fromabout 120° C. to about 250° C. For gas phase processes, it is preferredthat the temperature generally be within a range of about 60° C. to 120°C., and that the operating pressure be from about 5 bar to about 50 bar.

In addition to polyolefins, numerous other olefin derivatives may beformed from the ethylene and propylene, as well as C₄ ⁺ olefins,particularly butylene, separated according to this invention. Theolefins separated according to this invention can also be used in themanufacture of such compounds as aldehydes, acids such as C₂-C₁₃ monocarboxylic acids, alcohols such as C₂-C₁₂ mono alcohols, esters madefrom the C₂-C₁₂ mono carboxylic acids and the C₂-C₁₂ mono alcohols,linear alpha olefins, vinyl acetate, ethylene dicholoride and vinylchloride, ethylbenzene, ethylene oxide, cumene, acrolein, allylchloride, propylene oxide, acrylic acid, ethylene-propylene rubbers, andacrylonitrile, and trimers and dimers of ethylene and propylene. The C₄⁺ olefins, butylene in particular, are particularly suited for themanufacture of aldehydes, acids, alcohols, esters made from C₅-C₁₃ monocarboxylic acids and C₅-C₁₃ mono alcohols and linear alpha olefins.

VIII. One Example of the Invention

One example of compressing an olefin stream is shown in the FIGURE.According to the FIGURE, an olefin stream is passed through a line 10and sent to a first stage compressor 12. The olefin stream is compressedto a pressure of 105 psia (724 kPa), and the compressed olefin streamexits the compressor 12 through a line 14 at a temperature of 243° F.(117° C.).

The compressed olefin stream is sent through the line 14 to a causticwash tower 16. A caustic solution is injected into the caustic washtower 16 to contact the compressed olefin. The wash solution removesvarious non-olefin impurities such as CO₂ from the olefin stream, andthe solution is removed from the caustic wash tower 16 through a line20. Caustic washed olefin is removed from the caustic wash tower 16through a line 22.

The caustic washed olefin is sent through the line 22 to a water washtower 24. Water is injected into the water wash tower 24 to contact theolefin. The water removes additional non-olefin impurities as well asentrained caustic, and the water is removed from the water wash tower 24through a line 28. Olefin is removed from the water wash tower 24through a line 30.

The compressed olefin stream, having been caustic and water washed, issent through the line 30 to a second stage compressor 32. The olefinstream is further compressed to a pressure of 315 psia (2,172 kPa). Thisfurther compressed stream exits the compressor 32 through a line 34 at atemperature of 248° F. (120° C.).

The compressed olefin in the line 34 is sent to a dryer bed 36, whichcontains a molecular sieve adsorbent for removing additional water andoxygenates from the compressed olefin stream. Following drying, thecompressed olefin is sent through a line 38 to a separation system 40.Light olefin leaves the separation system 40 through a line 42, andheavy olefin leaves the separation system through a line 44.

Having now fully described this invention, it will be appreciated bythose skilled in the art that the invention can be performed within awide range of parameters within what is claimed, without departing fromthe spirit and scope of the invention.

1. A process for making and separating an olefin stream comprising amixture of olefins into at least two olefin streams, the processcomprising the steps of: (a) providing an olefin stream to be separatedcomprising at least about 20 wt % of an olefin selected from the groupconsisting of ethylene, propylene and combinations thereof and notgreater than about 3.0 wt % dienes based on the total weight of theolefin stream; (b) compressing the olefin stream in a compressor systemhaving a first stage and a second stage to obtain a compressed olefinstream; and (c) separating the compressed olefin stream into at leasttwo olefin streams.
 2. The process of claim 1, wherein the olefin streamto be separated comprises from at least about 50 wt % to about 90%ethylene and propylene based on the total weight of the olefin stream.3. The process of claim 1, wherein the olefin stream exits the firststage of the compressor at a pressure of from about 75 psia (517 kPa) toabout 150 psia (1,034 kPa), and exits the second stage of the compressorsystem at a pressure of at least about 175 psia (1,207 kPa), and thecompressed olefin stream exits the compressor system at a temperature offrom about 220° F. (104° C.) to no greater than about 260° F. (127° C.).4. The process of claim 3, wherein the olefin stream to be separated isproduced by the step of contacting an oxygenate with a molecular sievecatalyst comprising a silicoaluminophosphate or an aluminophosphate. 5.The process of claim 1, wherein the at least two olefin streams include(i) a light olefin stream comprising at least one olefin selected fromthe group consisting of ethylene, propylene and butylenes, and (ii) aheavy olefin stream comprising olefins that have boiling points thatare, on average, higher than those in the light olefin stream.
 6. Aprocess for making and separating an olefin stream comprising a mixtureof olefins into at least two olefin streams, the process comprising thesteps of: a) providing an olefin stream to be separated comprising atleast about 20 wt % of an olefin selected from the group consisting ofethylene, propylene and combinations thereof and not greater than about3.0 wt % dienes based on the total weight of the olefin stream; b)compressing the olefin stream in a compressor system having a firststage and a second stage to obtain a compressed olefin stream, whereinthe compressed olefin stream exits the first stage and the second stagea temperature of not greater than about 260° F. (127° C.) and exits thesecond stage a pressure of at least about 175 psia (1,207 kPa); and c)separating the compressed olefin stream into at least two olefinstreams.
 7. The process of claim 6, wherein the olefin stream beingcompressed in step b) is treated between the first stage and the secondstage to remove acid gases prior to separating the compressed olefinstream into at least two olefin streams.
 8. The process of claim 7,wherein the treated olefin stream is further washed with water prior toseparating into the at least two olefin streams.
 9. The process of claim6, wherein the process further comprises drying the compressed olefinstream formed in step b), prior to the separating in step c).
 10. Theprocess of claim 9, wherein the compressed olefin stream is contactedwith an adsorbent to dry the compressed olefin stream.
 11. The processof claim 6, wherein the at least two olefin streams include (i) a lightolefin stream comprising at least one olefin selected from the groupconsisting of ethylene, propylene and butylenes, and (ii) a heavy olefinstream comprising olefins that have boiling points that are, on average,higher than those in the light olefin stream.
 12. A process for makingand separating an olefin stream comprising a mixture of olefins into atleast two olefin streams, the process comprising the steps of: a)contacting an oxygenate with a molecular sieve catalyst to produce anolefin stream to be separated comprising at least about 20 wt % of anolefin selected from the group consisting of ethylene, propylene andcombinations thereof and not greater than about 3.0 wt % dienes based onthe total weight of the olefin stream; b) compressing the olefin streamin a compressor system having a first stage and a second stage to obtaina compressed olefin stream, wherein the compressed olefin stream exitsthe compressor system at a temperature of not greater than about 260° F.(127° C.) and exits the second stage a pressure of at least about 175psia (1,207 kPa); and c) separating the compressed olefin stream into atleast two olefin streams.
 13. The process of claim 12, wherein thecompressed olefin stream exits the first stage of the compressor at apressure of from about 75 psia (517 kPa) to about 150 psia (1,034 kPa).14. The process of claim 12, wherein the olefin stream to be separatedcomprises from at least about 50 wt % to about 90% ethylene andpropylene based on the total weight of the olefin stream.
 15. Theprocess of claim 12, wherein the olefin stream being compressed in stepb) is treated between the first stage and the second stage to removeacid gases prior to separating the compressed olefin stream into atleast two olefin streams.
 16. The process of claim 12, wherein thetreated olefin stream is further washed with water prior to separatinginto the at least two olefin streams.
 17. The process of claim 12,wherein the process further comprises drying the compressed olefinstream formed in step b), prior to the separating in step c).
 18. Theprocess of claim 12, wherein the at least two olefin streams include (i)a light olefin stream comprising at least one olefin selected from thegroup consisting of ethylene, propylene and butylenes, and (ii) a heavyolefin stream comprising olefins that have boiling points that are, onaverage, higher than those in the light olefin stream.
 19. The processof claim 12, wherein the molecular sieve catalyst is asilicoaluminophosphate or an aluminophosphate.
 20. A process for makingand separating an olefin stream comprising a mixture of olefins into atleast two olefin streams, the process comprising the steps of: a)providing an olefin stream to be separated comprising not greater thanabout 3.0 wt % dienes based on the total weight of the olefin stream; b)compressing the olefin stream in a compressor system having a firststage and a second stage to obtain a compressed olefin stream; and c)separating the compressed olefin stream into at least two olefinstreams.
 21. The process of claim 20, wherein the olefin stream exitsthe first stage of the compressor at a pressure of from about 75 psia(517 kPa) to about 150 psia (1,034 kPa), and exits the second stage ofthe compressor system at a pressure of at least about 175 psia (1,207kPa), and the compressed olefin stream exits the compressor system at atemperature of from about 220° F. (104° C.) to no greater than about260° F. (127° C.).
 22. The process of claim 21, wherein the olefinstream being compressed in step b) is treated between the first stageand the second stage to remove acid gases prior to separating thecompressed olefin stream into at least two olefin streams.
 23. Theprocess of claim 22, wherein the treated olefin stream is further washedwith water prior to separating into the at least two olefin streams. 24.The process of claim 20, wherein the process further comprises dryingthe compressed olefin stream formed in step b), prior to the separatingin step c).
 25. The process of claim 20, wherein the at least two olefinstreams include (i) a light olefin stream comprising at least one olefinselected from the group consisting of ethylene, propylene and butylenes,and (ii) a heavy olefin stream comprising olefins that have boilingpoints that are, on average, higher than those in the light olefinstream.